Process of preparing acetic anhydride



Patented Nov. 2 7, 1934 1,982,154 PROCESS OF PREPARENG ACETIO ANHYDRID Alfred Dierichs, Leverkusen-on-the-Bhine, and Leonhard Weiss, Wiesdorf, Germany, assignors to I. G. Farbenindustrie Frankfort-on-the-Main,

tion of Germany No Drawing.

Serial No. 514,692. 1929 Application Aktiengesellschaft, Germany, a corpora- February 9, 1931,

In Germany August 1,

12 Claims. (01. 260-123) The present invention relates to the manufacture of acetic anhydride by the catalytic decomposition of acetic acid.

It is known that acetic anhydride can be manufactured by leading acetic acid vapors over or through a catalyst containing phosphoric acid compounds as for instance molten phosphates, especially a molten mixture of sodium and lithium meta phosphate at temperatures between 500 C. and 1000 C. The reaction being an endothermic one the addition of heat is necessary.

According to the present invention molten metal phosphates are used as catalysts and the heat necessary for carrying out the reaction is supplied by using the molten catalyst as a resistance in an electric circuit. A simple method of carrying out the invention is to use the vessel containing the molten catalyst as one electrode and the tube by which the acetic acid vapors are introduced as the other electrode. The vessel and inlet tube are prepared from substances conducting an electric current, for instance metals, alloys, coal, graphite, carborundum, chamottegraphite and similar materials.

Any metal phosphate or mixture of metal phosphates may be used with or without boron phosphate and/0r boric acid anhydride. Examples of suitable metal phosphates are the alkali metal phosphates and especially heavy metal phosphates and also mixtures of heavy metal phosphates with boron-phosphate and boric acid anhydride. For instance, sodium-, lithium-, leadand zinc-meta-phosphates can be used as catalysts; also mixtures of lead-meta-phosphate with boron-phosphate or mixtures of zincand leadmeta-phosphate or mixtures of heavy metal phosphates and earth alkali metal phosphates, such as calcium and also aluminium or magnesium phosphate can be used in admixture with boric acid anhydride with or without the addition of boron-phosphate.

The. metal phosphates other than the alkali metal phosphates possess substantially the same efiicacy as the alkali metal phosphates, but ofler a higher specific resistance to the passage of the electric current and thus exhibit distinct advantages. Thus, for instance, a higher electrical potential can be applied and, consequently, the process is highly improved.

It is evident that the metal phosphates other than the alkali metal phosphates, for instance, the heavy metal phosphates, can also be applied in mixture with the alkali metal phosphates.

The present process has the advantage over all other processes used up to date, wherein-the heat required is supplied from the outside by means of gas, oil or electrical heating or by a The invention is illustrated by the following examples without being restricted thereto:

Example 1.-Into a copper crucible of 60 mm. diameter containing a molten mixture of equal parts (400 grams each of sodium meta phosphate and lithium meta phosphate) is introduced acetic acid vapor,'the temperature of the melt being 640 C., by meansof a copper inlet tube having a diameter of mm. The tube reaches mm. into the melt. The copper inlet tube is one electrade and the copper crucible the other electrode, the circuit having a voltage of 9.6 volts alternating current and the internal current being about 150 amperes. The yield of anhydride, containing only traces of phosphoric acid and organic compounds of phosphorus is -60% of the theoretical.

Example 2.-Into a crucible of chromium nickel steel of the Krupp A. G. (V4A), see German Patents Nos. 304,126; 304,159; 395,044; 399,806, of 160 mm. diameter containing a molten mixture of 1 part by weight .of sodium meta phosphate, 1 part by weight of lithium meta phosphate and 1 part by weight of borylphosphate '(boronphosphate B2O3.Pz'05) is introduced. Into the melt having a temperature of about IOU-750 C., acetic acid vapor having a temperature of about 620 C. isintroduced by means of an inlet tube made of V4A-steel dipping 50 mm. into the molten catalyst. Inlet tube and crucible form the electrodes. Alternating current is used, the voltage being 28-35 volts at 100-150 amperes. The yield and purity of the acetic anhydride produced are equal to the yield and purity of the product of Example 1. The addition of boronphosphate not 2. only prolongs the life period of the catalyst but also raises the specific resistance of the melt. As a result a higher amperage can be used.

The scope of the invention is illustrated by comparison of the specific resistances given in the following table:-

Specific resistance Catalysts at 750 0. "measured in ohms Sodium metaphosphate -L... 2. 1 Sodium lithium metaphosphate 2. 3 Sodium lithium metaphosphate with 4 6 boron phosphate Sodium lithium metap osphate with the addition of 30% boric acid anhydride 5. 2 Sodium lithium metaphosphate with the 30% boron phosphate and 5% ferric phosphate 5.8 Lead metaphosphate (according to manufacture) 7. 2'33 Zinc metaphosphate (according to manufacture) 10.4-130 1 part of boron phosphate and 4 parts of lead metaphosphate a 10 466,573, filed July 8, 1930 in which the use of a molten catalyst comprising an alkali-metal phosphate is claimed.

I tric current. a

We claimz- T l. Process of preparingacetic acid anhydride by the catalytic decomposition of acetic acid vapor, which comprises conducting said acetic acid vapor through a molten. catalyst comprising a metal phosphate, whichcatalyst is arranged as a resistance in an electric circuit and thus maintained at a temperature of between 500 and 1000 C. by means of an electric current. v

i 2. Process of preparing acetic acid anhydride by the catalytic decomposition of acetic acid vapor, which comprises conducting said acetic acid vapor through a molten catalyst comprising a metal phosphate and boron phosphate, which catalyst is arranged as a resistance in an electric circuit and thus maintained at a temperatureof between 500 and 1000 C. by means of an elec- 3. Process of preparing acetic acid anhydride by the catalytic decomposition ofacetic acid vapor, which comprises conducting said acetic acid vapor through a molten 'catalystcomprising a metal phosphate, boron phosphate and boric acid anhydride, which catalyst is arranged asa resistance in an electric circuit and 'thus maintained at a temperature of between 500 and 1000 C. by means of an electric'current.

4. Process of preparing acetic acid anhydride by the catalytic decomposition of acetic acid vapor, which comprises conducting said acetic acid vapor through a molten catalyst comprising a heavy metal phosphate, which catalyst is arranged as a resistance in an electric circuit-and thus maintained at a temperature'of between 500 and 1000 C. by means of an electric circuit.

' 5. Process of preparing acetic acid anhydride by the catalytic decomposition of acetic acid vapor, which comprises conducting said acetic acid The present application is a continuation in part application of our application'Serial No.,

by the catalytic decomposition of acetic acid vapor, which comprises conducting said acetic acid vaporthrough a molten catalyst comprising a heavy metal phosphate and an alkali metal phosphate, which catalyst is arranged as a resistance in an electric circuit and thus maintained at a temperature of between 500 and 1000 C. by

means of an electric current.

8. Process of preparing acetic acid anhydride by the catalytic decomposition of acetic acid vapor, which comprises conducting said acetic acid vapor through a molten catalyst comprising a heavy metal phosphate, an alkali metal phosphateand boron phosphate, which catalyst is arranged as a resistance in an electric circuit and thus maintained at a; temperature of between 500 and 1000 C. by means of an electric current.

9. Process of preparing acetic acid anhydride by the catalytic decomposition of acetic acid vapor,- which comprises conducting said acetic acid vapor through a molten catalyst. comprising a heavy metal phosphate, an alkali metal phosphate, boron phosphate and boric acid anhydride, which catalyst'is'arranged as a resistance in an electric circuit'and thus maintained at a temperature of between 500 and 1000 C. by means of an'electric current. 10. Process of preparing acetic acid anhydride by the catalytic decomposition of acetic acid vapor, 'whichcomprises conducting said acetic acid.

vapor through a molten catalyst comprising leadmeta phosphate, which catalyst is arranged as a resistance in an electric circuit and thus maintained at a temperature of between 500 and 1000 C. by means of an electric current.

11. Process of preparing acetic acid anhydride by the catalytic decomposition of acetic acid .va por, which comprises conducting said acetic acid vapor through a molten catalyst comprising zincmeta phosphate, which catalyst is arranged as a resistance in an electric circuit and thus maintained at a temperature of between 500 and 1000 C. by means of an electric current.

12. Process of preparing acetic acid anhydride by the catalytic decomposition of acetic acid vapor, which. comprises conducting said acetic acid, vapor througha molten catalyst comprising leadmeta phosphate and boron phosphate, which catalyst is arranged as a resistance in an electric.

circuit and thus maintained at a temperature of between 500 and 1000 C. by means of an electric current. .v 1

ALFRED DIERICHSQ LEONHARD WEISS. 

